[Rockhounds] "Petrified algae"

Thomas Yancey teyancey at suddenlink.net
Sun Feb 3 21:45:55 PST 2013


Pete and others,

The problem here is the use of the words "petrified algae", that 
conjures up an image of pieces of wood covered with green plants. The 
Green River Formation contains calcareous lake deposits where many 
things could be covered with encrusting layers, but much of 
encrustation is probably due to a mix of microbes and inorganic 
cement. Some layers of the formation do contain stromatolites formed 
by mats of microbes trapping sediment. Other parts of the lake appear 
to have precipitated carbonate mud. These things are not examples of 
petrification like the process that preserves bone or wood, they 
simply are crusts of sediment layers that become well cemented. The 
process is more like the formation of travertine where carbonate 
forms crusts and layers on any object that is in contact with water. 
The wood could petrify, not the rind. Also, the microbes present may 
be entirely non-algal types. It is often assumed that stromatolite 
mats are formed of blue-green algae (cyanobacteria), yet studies of 
living mats often reveals few or no blue-greens present.

Because the woods you are describing are replaced with blue silica, 
much of original structure has been lost. Why not just call the rind 
"lake crust"?

Tom Yancey



>I ditto, would be curious for some verified paleontological 
>information about the "petrified algae" too.
>
>P.S., dunno about you rockhounds... exchanging all these messages, 
>right through the Superbowl...  Axel is excused from that, of course.
>  (it was pretty one sided for a while, but things have picked up...)
>
>Cheers, Pete
>
>-----Original Message-----
>From: Tim Fisher <nospam at orerockon.com>
>To: 'Rockhounds at drizzle.com: A mailing list for rock and gem 
>collectors' <rockhounds at lists.drizzle.com>
>Sent: Sun, Feb 3, 2013 6:01 pm
>Subject: Re: [Rockhounds] right through the middle! and pet wood
>
>
>I would like to see something concrete about the "petrified algae". That has
>long been the explanation for the thick rind around most of the limbs but I
>have never seen verification of this. I'm skeptical since the surrounding
>material looks more like volcanic ash than waterborne sediments to me. Which
>makes sense since the deposit is squarely in the middle of the Green River
>Fm., which is a large lake basin ("Fossil Lake") that periodically got wiped
>out by volcanic ash falls. I suppose that wood covered with algae could be
>covered in ash and fossilized, but that's an awful think coating of algae.
>Some of it is 4 or more times the diameter of the limbs. On the other hand
>an excellent paper was written about the species to be found there, and
>there are quite a few of them. A lot of what I have dug is the type with
>"joints" every 12-14" or so, like bamboo. That's usually the reason it comes
>out in pieces. It's been identified as an extinct relative of the
>balloonvine, Cardiospermum, which is really a small and insubstantial vine.
>In contrast the limbs can get as much as 2-4" thick which would make it a
>giant, more like rattan.
>
>There are also "petrified termite mounds" just to the SW of the Blue Forest
>area that I sincerely doubt are any remnant of insect nests. I don't have
>any other explanation, other than they look like the WY "fossil
>stromatolites" more than anything else. Although I haven't seen anything
>definitive about those either.



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